Bran flakes may be classed as junk food under new government reforms designed to promote healthy eating.

Britain has for decades been one of the world’s largest consumers of puffed, flaked and sugared breakfast cereals, despite warnings over the years that they might not be nutritious.

Officials want to update the UK nutrient profiling model (NPM) to include naturally occurring “free sugars”, alongside refined sugar, when determining what is healthy or unhealthy.

Bran flakes typically contain added glucose from natural ingredients such as corn or wheat starch to make them more palatable, so it is likely they will be deemed a “high in fat, salt or sugar” (HFSS) food under the new system.

Dean O’Brien, the managing director of Kellanova (formerly Kellogg Company), told the Telegraph the proposed plans had “the potential to unintentionally undo years of work and investment by food companies to encourage healthier choices”.

“Over the last decade, Kellogg’s has reduced sugar by 27% and salt by 22% in its cereals, and under current regulations all of our children’s cereal, and four of our five bestsellers, are deemed healthy.

“However, under the newly proposed plans, cereals such as bran flakes, which are high in fibre and low in saturated fat, would be re-classified as less healthy.”

O’Brien added that breakfast cereals are “nutritionally dense” and Kellogg’s cereals are “fortified with vitamins and iron”.

A government spokesperson said previous nutrition rules were 20 years old and did not “reflect the latest dietary advice”, adding that the “new model shifts the focus from total sugars to free sugars and promotes diets higher in fibre”.

“Obesity and poor diets rob children of the best possible start in life, and this is about supporting parents to raise the healthiest generation of children by restricting the advertising and promotion of junk food,” they added.

“We are currently consulting on applying the new model to the advertising and promotions restrictions and will consider all feedback.”

It is not the first time popular cereals have been flagged by nutritionists. In 2009, a survey by the consumers’ organisation Which? of 100 cereals found typical portions of some were found to contain more sugar than a Cadbury chocolate Flake, despite manufacturers’ claims to be reducing the level of unhealthy ingredients.

Many brands perceived to be healthy, including Kellogg’s All Bran, Bran Flakes and Special K, also had high levels of sugar at the time.